The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services from geostationary orbit. The present invention relates to a spacecraft radiator system including a crossing heat pipe system that utilizes heat pipes to thermally couple radiator panels on a satellite or spacecraft equipment panels that may or may not radiate to space. The heat pipes are used to transfer and distribute thermal energy from heat sources such as operating electronic heat dissipating units to and across radiator panel surfaces from where it may be radiated into space. When the spacecraft is operating on-orbit, the radiator panels, generally, will be disposed in a north or south facing direction, because the north or south panels experience a solar radiation exposure that is relatively benign and stable compared to non-radiating panels. Non-radiating equipment panels may be interior to the spacecraft and/or face in an east/west or Earth/anti-Earth direction and experience significant diurnal cycles as the spacecraft orbits the Earth.
A better appreciation of the presently disclosed techniques may be obtained by referring first to FIG. 1 which illustrates some typical features of a known spacecraft radiator system including crossing heat pipes. For clarity of illustration, a simplified view of a spacecraft radiator system 30 is illustrated that omits spacecraft components not directly related to the spacecraft radiator system. The illustrated spacecraft radiator system 30 includes North radiator panel 11a and South radiator panel 11b. A transverse panel 12 is disposed between and structurally coupled with North radiator panel 11a and South radiator panel 11b. The transverse panel 12 may be, as shown in the illustrated example, orthogonal to the spacecraft yaw axis and may, accordingly, be facing in the Earth or anti-Earth direction. The presently disclosed techniques also contemplate that the transverse panel 12 may be parallel to the spacecraft yaw axis, in which case the transverse panel 12 may be referred to as an East/West panel.
A number of parallel heat pipes 15 may be disposed such that transverse panel 12 is thermally coupled with North radiator panel 11a and with South radiator panel 11b. More particularly, a heat pipe 15 may be configured in an ‘L’ shape such that a first section 151 is thermally coupled with North radiator panel 11a or South radiator panel 11b and a second section 152 is thermally coupled with the transverse panel 12. As illustrated, the first section 151 may be disposed near or within North radiator panel 11a and the second section 152 transverse to the first section 151 may be disposed near or within transverse panel 12. Heat dissipating components and equipment 19 may be mounted on the inner panel surfaces 17 of the North radiator panel 11a, the South radiator panel 11b and/or the transverse panel 12.
A transverse section 152a of heat pipe 15a extending from the North radiator panel 11a is illustrated as being adjacent to a transverse section 152b of heat pipe 15b extending from the South radiator panel 11b. The adjacent transverse sections 152a and 152b may be said to overlap and may be respectively thermally coupled. Additionally, the transverse sections 152a and 152b may be used to transfer thermal energy between heat dissipating units mounted on the transverse panel 12 on the one hand and the North and/or South radiator panels on the other hand.
Referring to View A-A, it may be observed that an axial cross section of heat pipe 152 includes axial grooves, disposed between fins or splines 153. Each heat pipe typically constitutes a closed, self-contained vessel filled with a predetermined amount of an appropriate fluid, such as ammonia, toluene, or a water/isopropyl alcohol mixture. The fluid in the heat pipe members may be in a partially liquid and a partially gaseous state. The extent and location of liquid state fluid and gaseous state fluid will depend on the temperature of environments to which various parts of the heat pipe are exposed.
In a zero-g environment, as experienced on orbit, capillary action is effective to transport liquid state fluids along the axial length of the heat pipe. As a result, heat transfer between heat dissipating units and north/south radiator panels may be relatively efficient.
In a 1-g environment, as experienced during spacecraft ground testing, capillary action is not effective to the extent that the axial length of a heat pipe is inclined relative to horizontal. As a result, during ground testing, liquid state fluid tends to “puddle” in the lower portions of the heat pipe. More particularly, referring now to FIG. 2, when the spacecraft radiator system 30 is oriented with North radiator panel 11a vertically above South radiator panel 11b, a lower region of transverse panel 12 includes heat pipes with wetted portions and an upper region of transverse panel 12 includes only heat pipes without wetted portions. For example, as maybe observed in view B-B only the lower portion of heat pipe 15a and heat pipe 15b is wetted. Similarly, when the spacecraft is oriented with South radiator panel 11b vertically above North radiator panel 11a, an upper region of transverse panel 12 includes only heat pipes without wetted portions.
Consequently, heat dissipating units are conventionally disposed only proximate to the north/south mid-point of the transverse panel, within approximate region 120, so as to ensure that heat dissipating units are always proximate to a wetted portion of at least one heat pipe. Otherwise, operation of heat dissipating units during ground, functional and environmental testing, for example, may result in overheating of such heat dissipating units.
As a result, an improved approach to crossing heat pipe design is desirable.